The present invention relates to a hydrocracking catalyst and its preparation process, especially a highly active midbarrel hydrocracking catalyst and its preparation process.
In recent years, the demand in both domestic and worldwide markets for high quality middle distillate products has been continuously increasing and the gap between supply and demand is getting greater and greater along with the development of the economy. The hydrocracking technology has become an optimum means for producing high quality clean middle distillates through deep processing of heavy oils due to its unique advantages.
At present, the activity of the midbarrel hydrocracking catalyst is not very high, and the solidifying point of the derived diesel with a wide distillation range is relatively high, so it is difficult to attain the objective of further increasing the output of the middle distillate oils by modifying the existing device or increasing the throughput.
The key to the increase in the output of the middle distillates in hydrocracking lies in the development and application of an adequate catalyst. The activity and selectivity to the middle distillates of a hydrocracking catalyst containing a single sort of zeolite can not be raised to a maximum extent due to the restriction of the sort of the zeolite, while the activity and selectivity to the middle distillates of a hydrocracking catalyst containing a composite of zeolites can be remarkably raised since the characteristics of various sorts of zeolites may be fully developed and synergetic catalysis may occur.
U.S. Pat. Nos. 5,536,687, 5,447,623 and 5,350,501 disclose a catalyst containing a zeolite-P and a zeolite-Y which is zeolite UHP-Y (LZ-10), which is prepared by (1) lowering the content of Na2O to 0.6-5.0 wt. % by partial NH4+ exchange of the zeolite-NaY, (2) lowering its unit cell size to 24.40-24.64 xc3x85 by steam calcination treatment, (3) lowering the content of Na2O to  less than 0.5 wt. % by the second time NH4+ exchange, (4) lowering its unit cell size to 24.25-24.35 xc3x85 by steam calcination treatment again. The catalyst for producing middle distillates comprises zeolite-Y (1-15 wt. %), zeolite-xcex2 (1-15 wt. %), dispersed silica-alumina, alumina, metals W and Ni. Its activity and selectivity to middle distillates are not so high, so it is difficult to meet the need of producers for increasing the processing capacity of the device to further increase the output of middle distillates.
U.S. Pat. No. 5,279,726 discloses a hydrocracking catalyst containing a zeolite-xcex2 and the use thereof, which catalyst contains a zeolite-xcex2 and a zeolite-Y which is a ultra-stable zeolite-Y (LZY-82, LZY-84) with a unit cell size of 24.52-24.59 xc3x85. The catalyst for producing middle distillates contains zeolite-Y and zeolite-xcex2 of 2.5-15 wt. % respectively. The zeolite-Y of the catalyst has a large unit cell size and strong acidity, which is unfavorable to the increase in the selectivity of the catalyst to middle distillates.
U.S. Pat. No. 5,160,033 discloses a hydrocracking catalyst for improving the octane number of gasoline and a process for the preparation thereof, which catalyst takes a zeolite-Y and a zeolite-xcex2 as the acidic components and is mainly used in the isomerization of alkanes. The zeolite-xcex2 is calcined to weaken its acidity, and the zeolite-Y is a ultra-stable zeolite Y-85 with a silica to alumina ratio of 6.5-20 and a unit cell size of 24.34-24.58 xc3x85. The catalyst contains 10-30% of zeolite-xcex2 based on the total amount of the zeolites. This catalyst is mainly used in the isomerization of alkanes in gasoline.
U.S. Pat. No. 5,464,527 discloses a hydrocracking catalyst for raising the selectivity to middle distillates (turbine fuel+diesel), which catalyst uses a ultrahydrophobic zeolite-Y exchanged with rare earth (LZ-10) and dispersed silica-alumina as cracking components, and the metals W and Ni as hydrogenation metal components. This catalyst has a high selectivity to middle distillates, but its reaction temperature is still high.
The object of the present invention is to overcome the drawbacks of the prior catalysts and to develop a hydrocracking catalyst with a high activity and high yield to middle distillates.
The inventors have now surprisingly discovered a hydrocracking catalyst which has an activity higher than those of the prior midbarrel catalysts, and a remarkably increased selectivity to middle distillates. The solidifying point of the produced diesel distillate is lowered. This catalyst can meet the need of the refineries for increasing the throughput and further increasing the output of the middle distillates.
The hydrocracking catalyst of present invention comprises zeolites, amorphous silica-alumina and alumina as a support, Group VIII metal(s) and/or Group VIB metal(s) as active components; and comprises, on the basis of the catalyst weight, 4%-28%, preferably 4%-25% of a modified zeolite-Y and 4%-28%, preferably 4%-18% of a modified zeolite-xcex2, wherein said zeolite-Y has a relative crystallinity of higher than 95%, preferably 100%-105%; a silica/alumina molar ratio of 9.0-30.6, preferably 10-20; an infrared acid of 0.30-0.90 mmol/g with more than 95% of Bronsted acid; an unit cell size of 24.25xc3x9710xe2x88x9210 m-24.45xc3x9710xe2x88x9210 m; a Na2O weight content of less than 0.16%, preferably less than 0.1%. Said modified zeolite-xcex2 has a silica/alumina molar ratio of 85-153, preferably 102-136; a Na2O weight content of less than 0.15%, preferably less than 0.1%; a relative crystallinity of 100-110% and an infrared acid of 0.1-0.4 mmol/g, preferably 0.2-0.3 mmol/g.
Said zeolite-Y preferably has a specific surface area of 680-850 m2/g, and a pore volume of 0.30-0.55 ml/g; said modified zeolite-p preferably has a specific surface area of 400-750 m2/g, more preferably 500-600 m2/g, and a pore volume of 0.25-0.50 ml/g, preferably 0.3-0.4 ml/g.
Said catalyst generally comprises amorphous silica-alumina of 0-32%, preferably 10%-28%; macroporous alumina of 0-32%, preferably 7%-28%; microporous alumina of 12-18%, preferably 13%-16%; Group VIB metal(s) of 15%-30%, preferably 18%-27%; Group VIII metal(s) of 3%-8%, preferably 4%-7%.
The aforesaid modified zeolite-Y may be derived by modification of zeolite-SSY. Particularly, said modified zeolite-Y may be prepared by calcining the zeolite-SSY in the presence of steam at a temperature of 500xc2x0 C.-750xc2x0 C., preferably 550xc2x0 C.-650xc2x0 C. under a vapor pressure of 0.01-0.30 MPa, preferably 0.05-0.20 MPa for 0.5-4 hours, preferably 1-2 hours.
Said zeolite-SSY may be prepared by
(1) mixing a starting material of zeolite-Y (i.e., zeolite NH4NaY or NaY) with water to form a slurry of the zeolite, the concentration of which is that per 100 ml slurry contains 5-30 g, preferably 10-25 g of the starting material of zeolite-Y;
(2) heating the mixture of step (1) to a temperature of 50-120xc2x0 C., preferably 70-100xc2x0 C.;
(3) adding thereto the crystal ammonium hexafluorosilicate or a solution thereof, and reacting with stirring the mixture for 0.1-24 hours, preferably 0.5-5 hours; and
(4) separating the product, which is then filtered, washed with water, and dried to obtain said zeolite-SSY; wherein
in step (1) the starting material of zeolite-Y is preferably zeolite NH4NaY with its Na2O content of less than 5.0% by weight, and its silica/alumina molar ratio of 3.5-7.0, preferably 4.5-7.0; and
in step (3) the amount of the added ammonium hexafluorosilicate is at least 10 g, preferably 20-50 g relative to per 100 g starting material of zeolite-Y; and the addition rate is up to 30 g, preferably 5-25 g per hour relative to 100 g of the starting material of zeolite-Y.
The zeolite-SSY with low Na2O content and high crystallinity is obtained directly by the above process.
The aforesaid modified zeolite-p may be a new one derived by the following highly efficient synthesis process, which comprises the steps that
(1) a slurry of a completely crystallized zeolite-xcex2 is directly subjected to ammonium salt exchange;
(2) the ammonium salt exchanged zeolite-xcex2 is filtered, washed with water, dried and calcined;
(3) the calcined, deammoniated zeolite-xcex2 is treated with an acid; and
(4) the acid treated zeolite-P is subjected to a pressurized steam calcination treatment.
In aforesaid step (1), the completely crystallized zeolite-xcex2 is generally synthesized by hydrothermal synthesis with an organic amine as a template, said crystallized zeolite-P generally has SiO2/Al2O3 ratio of 42-51 and Na2O content of 3.0 wt. %-4.0 wt. %. The characteristic of step (1) is to combine the mother liquor separation with ammonium salt exchange into one step, wherein the original slurry is diluted with pure water to a solid/liquid ratio of 1:8-1:15 by weight and then an ammonium salt is added to make its concentration in the solution attain 0.1-10.0 mol/l, preferably 0.5-5.0 mol/l. Then the ammonium salt exchange is carried out. The ammonium salts used may be ammonium nitrate, ammonium chloride, ammonium sulfate, etc. The solution is fully stirred while conducting the exchange, and the temperature is maintained in a range from room temperature to 100xc2x0 C. for 0.5-5.0 h, preferably 1.0-3.0 h. The concentration of the zeolite in the slurry is controlled in 0.01-1.0 g/ml, preferably 0.05-0.5 giml so that the Na2O content in the exchanged zeolite does not exceed 0.5% by weight. The requirement can usually be fulfilled when step (1) is carried out twice.
In aforesaid step (2) the ammonium salt exchanged zeolite-xcex2 is generally filtered, washed with water, dried to a weight content xe2x89xa780% on dry basis, and then subjected to deammoniation by calcination. Said calcination is preferably carried out stepwise in a calcination furnace with air flowing therethrough. The first step of calcination is carried out at 150xc2x0 C.-250xc2x0 C. for 2.0-4.0 h to remove the remaining water, the second step at 250xc2x0 C.-450xc2x0 C. for 4.0-6.0 h to decompose the organic amine, and the third step at 450xc2x0 C.-650xc2x0 C. for 5.0-15.0 h to remove the free carbon.
In aforesaid step (3) the acid treatment is generally carried out with fully stirring with an inorganic acid of 0.05-10.0 moll, preferably 0.1-5.0 mol/l. The particular conditions are: temperature 20xc2x0 C.-100xc2x0 C.; duration 0.5-5.0 h, preferably 1.0-3.0 h; the concentration of the zeolite in the slurry 0.01-1.0 g/ml, preferably 0.05-0.5 g/ml; the pH value of the slurry is controlled at 1.5-3.5, The inorganic acid used can be hydrochloric acid, nitric acid, sulfuric acid, etc.
In aforesaid step (4) the pressurized steam calcination treatment is generally carried out by putting the acid treated sample in a sealed steam calcination treatment furnace and raising the temperature to 500xc2x0 C.-800xc2x0 C. with a heating rate of 100-600xc2x0 C./h, preferably 200-400xc2x0 C./h. The temperature for the steam calcination treatment is preferably 550xc2x0 C.-630xc2x0 C. and the pressure of the system is 0.05-0.50 MPa, preferably 0.10-0.20 MPa. These conditions are maintained for 0.5-5.0 h, preferably for 1-2 h. Then the pressure is released and the temperature is lowered down to yield the modified zeolite-xcex2 of the present invention.
In aforesaid step (3), after acid treatment, an ammonium salt may be added to the slurry of the zeolite-xcex2 so that the concentration of the ammonium salt in the slurry attains 0.2-0.6 mol/l, and then the slurry is filtered. Said ammonium salts can be ammonium nitrate, ammonium chloride, ammonium carbonate, ammonium sulfate, etc.
In aforesaid step (3) the filtered zeolite-xcex2 can be directly calcinated in the presence of steam. It is preferred to dry it to a material of 80 wt. %-90 wt. % on dry basis, then uniformly spray pure water on to said material (0.2-0.6 kg/kg material), and carry out the steam calcination treatment.
The characteristics of the modified zeolite-p prepared by the above process are an adequate acidity, uniform distributed acidic sites, high crystallinity, and possession of more secondary pores and a small amount of non-framework aluminum.
The content of SiO2 in the amorphous silica-alumina according to the present invention is 20%-75%, preferably 35%-60% by weight, and the content of Al2O3 is 25%-80%, preferably 40%-65% by weight. The pore volume of the amorphous silica-alumina is 0.5-1.1 ml/g, preferably 0.6-0.8 ml/g. The specific surface area is 200-500 m2/g, preferably 280-500 m2/g. Said amorphous silica-alumina of the present invention may be prepared by coprecipitation or graft copolymerization.
The metals of Group VIII of the present invention are preferably Co and/or Ni, and the metals of Group VIB are preferably Mo and/or W.
The pore volume of the macroporous alumina used in the present invention is 0.6-1.2 ml/g, preferably 0.8-1.2 ml/g, and the specific surface area is 200-550 m2/g, preferably 300-500 m2/g.
The microporous alumina used in the present invention is used as a binder after peptization by inorganic and/or organic acids in the preparation of the catalyst. The pore volume of said microporous alumina is 0.3-0.5 ml/g and the specific surface is 180-350 m2/g. The inorganic acids used can be HCl, HNO3, H3PO4, or H2SO4, preferably HNO3 or H3PO4, and the organic acids can be acetic acid, propanoic acid, ethane diacid, and citric acid. When the binder is made, the ratio of the inorganic and/or organic acids to the microporous alumina (mol/mol) is generally 0.10-0.50, preferably 0.20-0.35.
The specific surface area of the catalyst of the present invention is 200-360 m2/g, and the pore volume is 0.30-0.50 ml/g.
The highly active midbarrel hydrocracking catalyst of the present invention may be prepared in the following steps:
(1) mixing the modified zeolite-Y, modified zeolite-xcex2, optional amorphous silica-alumina and macroporous alumina, microporous alumina, and extrusion aid, forming by extrusion, and drying;
(2) calcining the dried extrudates prepared in step (1) to form a support;
(3) impregnating the support prepared in step (2) with a solution containing active metal components, then drying, calcining to yield the catalyst of the present invention.
Particularly, the catalyst may be prepared as follows:
The modified zeolite-Y, modified zeolite-xcex2, optional amorphous silica-alumina and macroporous alumina, and extrusion aid are put into a comulling machine and comulled for 20-40 min. Then the microporous alumina is added and the comulling is continued for 25-40 min. Consequently, a certain amount of industrially pure water is added to the comulled material and the comulling is continued until the mixture becomes an extrudable paste. Now the content of dry basis in the paste is 38%-52% by weight of the whole paste. The paste is formed by extrusion, dried and made into dry bars. The dry bars are heated to 500xc2x0 C.-700xc2x0 C. along programmed temperature and calcined for 2.5-6 h.
Active metal components are at least one of the metals of Group VIB and at least one of the non-noble metal of Group VIII. In particular, Group VIII metals are preferably Co and/or Ni, and Group VIB metals are preferably Mo and/or W. Tungsten compounds used to prepare the solution are preferably ammonium metatungstate and/or tungstic acid and the molybdenum compounds may be one or more of various ammonium molybdates, molybdic acids and molybdenum oxides. Nickel compounds can be one or more of nickel nitrate, nickel acetate, and nickel basic carbonate. Cobalt compounds can be cobalt nitrate and/or cobalt acetate. Impregnation aids may be present in the impregnation solution and they can be inorganic acids, organic acids and/or salts of organic acids. The inorganic acids can be phosphoric acid, nitric acid etc, and the organic acids can be formic acid, acetic acid, citric acid, etc. The salts of organic acids can be ammonium formate, ammonium acetate, and ammonium citrate, etc.
The processes for impregnating the support can be saturation impregnation, supersaturating impregnation, or complexing impregnation. The duration of the impregnation is 1-12 h. The impregnated support is dried at 100xc2x0 C.-150xc2x0 C. for 1-12 h. The dried catalyst is calcined at 450xc2x0 C.-550xc2x0 C. for 2.5-6.0 h to yield the catalyst of the present invention.
The catalyst of the present invention is useful in the hydrocracking of heavy oils for producing middle distillates with a maximum output, especially in the production of high quality middle distillates by hydrocracking heavy oils with at least 50 v % of the distillate having a boiling range of 426xc2x0 C.-551xc2x0 C., a total sulfur content of 1.5%-3.0% by weight, and a total nitrogen content of 1300-2000 xcexcg/g.
When the catalyst according to the present invention is used in the hydrocracking of heavy oils for producing middle distillates, its activity is 8xc2x0 C-13xc2x0 C. higher than that of the prior midbarrel hydrocracking catalyst, and the selectivity to middle distillates is over 1.5 wt. % higher. The solidifying point of the produced diesel is lowered by 6xc2x0 C.-9xc2x0 C. The hydrogenation performance of the catalyst prepared according to the present invention is excellent, and the middle distillate products are high quality jet fuel and diesel.
The catalyst of the present invention and the process for the preparation thereof will be described in more detail in the following examples which should not be construed as any limitation to the protection scope of the appended claims.